Exemplary embodiments of the invention relate to a valve assembly for switching and/or regulating a medium flow of an aerospace engine, as well as to an aerospace engine.
Valves are generally used for switching or regulating the throughflow of a gaseous or liquid medium. Valve assemblies, which comprise solenoid valves, are usually used in aerospace engines. In these solenoid valves the medium that is to be regulated can be easily separated from a drive of the valve, a feature that is absolutely mandatory for use in aerospace engines due to the danger presented by the fuel. However, the medium flow can only be switched because solenoid valves have only the positions “open” or “closed.” In order to regulate the medium, these solenoid valves have to be clocked-operated, a feature that can be achieved in the field only with difficulty.
Therefore, exemplary embodiments of the present invention are directed to a valve assembly that is structurally and/or operationally improved, on that it is possible to regulate the medium, even when the medium to be regulated is strictly separated from the drive of the valve assembly. Further, exemplary embodiments of the invention are also directed to an aerospace engine, with which the fuel feed can be better regulated.
In accordance with exemplary embodiments of the present invention a valve assembly designed for switching and/or regulating a medium flow of an aerospace engine comprises a drive, a valve and a flexible separator element. The drive has one or more electrically actuatable actuators, which change their length in the direction of a longitudinal axis of the valve assembly when a control voltage is applied to the actuators. Hence, the drive is an electric drive. The valve comprises a valve piston, which can be moved back and forth along the longitudinal axis by means of the drive and which has a valve member. The flexible separator element delimits a working space of the valve from the drive, as a result of which the medium, which flows through the valve or is present in the working space, is hermetically separated from the drive.
The combination of an electric drive one or more electrically actuatable actuators makes it possible to regulate the medium in conjunction with the separator element, even when the medium to be regulated is strictly separated from the drive. The valve can be operated by means of the electric drive not just in the two positions “open” and “closed” alone. Instead, the position of the valve member between these end positions can be variably changed, so that the medium flow can be adjusted in a desired manner. The net result is that it is possible to prevent the drive from being damaged by the medium and to prevent the medium from escaping in an uncontrolled manner from the working space. Therefore, the valve assembly is suitable for hazardous mediums, such as rocket fuels.
In one embodiment the flexible separator element surrounds the valve piston and is connected fluid-tight to the valve piston with a drive-sided end. The flexibility of the separator element allows the valve piston to move, so that the valve can be moved, as required, between its end positions “open” and “closed,” by actuating the drive to match the requirements. At the same time the working space is separated from the drive.
The valve piston can have a piston plate, which extends perpendicular to the longitudinal axis of the valve assembly in a plane, so that the separator element is connected to the piston plate with the drive-sided end. This approach makes it easier to attach the separator element in such a way that it is fluid-tight.
In an additional embodiment the separator element is connected to a housing component of the drive or to a housing component of the valve with the valve-sided end. It is advisable that the diameter of the separator element at its drive-sided end correspond to the diameter at the valve-sided end. Thus, the separator element can have a somewhat cylindrical shape, a feature that greatly simplifies the geometric shape of the separator element.
The separator element can be a metal bellows. This arrangement ensures good stability in conjunction with the required flexibility. The separator element can also be a diaphragm.
The piston plate of the valve piston can be disposed in a housing shoulder, which extends in the direction of a drive housing and which is connected to the working space with its open end. The result is that when the valve is opened, the piston plate moves away from the working space in the direction of a shoulder plate of the housing shoulder, and that a first spring is disposed between the shoulder plate and the piston plate. This first spring presses the valve member against the valve seat, when a voltage is not applied to the actuator(s). The piston plate is used to offer the first spring an engagement face, which acts on the piston valve, in order to ensure that the valve member is pressed against the valve seat in, for example, a non-actuated state of the actuator(s).
In one embodiment the piston plate can be used not only for mounting the separator element, but also as an engagement face for the first spring. In another embodiment the piston plate can also be used only as an engagement face for the first spring. In this embodiment the separator element is mounted fluid-tight directly on the shank of the valve piston on the side that is located opposite the first spring.
The stroke of the valve piston between its end positions “closed” and “open” can be adjusted in a very simple way with high precision and with a minimum amount of energy, if the actuator(s) is or are a piezo actuator or piezo actuators, which changes or change its or their length when a voltage is applied to the actuator(s). If only one single piezo actuator is provided, then this actuator can be designed as a ring. If the drive comprises a plurality of piezo actuators, then they can be designed as a stack. The piezo actuators of the drive can be configured in a way, which is known to the person skilled in this art, in parallel or in series or in any combination thereof. The actuators are designed, in particular, in such a way that they expand, when a voltage is applied to them.
In an additional embodiment the actuator(s) is or are supported at its or their one end by a housing component, which is adjacent to the valve and is a part of the drive, or by a housing component of the valve. If the actuators expand when a voltage is applied to them, then the actuators expand in a direction facing away from the valve. The movement is transmitted to the valve piston, so that then the valve member moves away from the valve seat; and, as a result, the valve opens.
The actuator(s) is or are supported at its or their other end by a head plate, which is biased by a second spring. In this case the second spring applies a spring bias to the actuator(s). The head plate is pushed away from the valve, when the actuators expand as a voltage is applied to them. The force can be transmitted to the valve piston by way of the head plate.
For this purpose in one embodiment a valve piston head engages with the head plate. In this case the valve piston is guided through a bore in the head plate; and the valve piston head is connected to the valve piston on the side that is opposite the actuator(s). This arrangement ensures that the expansion of the actuators is transmitted, as described above, into the movement of the valve piston. The valve piston head can be disposed on the end of the valve piston that lies opposite the valve member. The valve piston head can be connected to the valve piston in a positive and/or non-positive manner.
The valve member can be, for example, a ball. The valve member can have a semi-spherical section, which faces the valve seat. The valve member can be a cone or a conical section, which faces the valve seat with its end that tapers to a point.
The valve assembly can comprise a device for determining an axial displacement of the valve piston. In this case a stroke, which can be determined by the device, can be made available for controlling the actuator(s). The result is that the stroke of the valve piston can be measured. The voltage source for actuating the actuator(s) can be controlled by feedback; and the length or more specifically the opening slit of the valve can be adjusted. This arrangement makes it possible to switch the valve not only between “open” (i.e., the maximum opening slit) and “closed,” but also to adjust, as required, the opening slit between the end positions. This feature makes it possible to regulate the medium flow.
In one embodiment the actuator(s) is or are arranged in such a way that when a voltage is applied to the actuator(s), the actuator(s) causes or cause the valve to open due to an elongation; and, when no voltage is applied to the actuator(s), the actuator(s) closes or close the valve.
Furthermore, exemplary embodiments of the invention are directed to an aerospace engine, which comprises at least one valve assembly of the type described above. In the case of such an aerospace engine the fuel feed can be regulated reliably and precisely in a simple way. Moreover, the aerospace engine has the above described advantages. An additional advantage of an engine system that is driven in this way is the ability to freely adjust the mixing ratio and the thrust, so that there is no need, among other things, for trimming diaphragms.